Generally, a two-cylinder rotary compressor is structured to perform the uncompressed operation of one of compression mechanisms in the low load state for the low performance operation so as to improve the operation efficiency.
Japanese Patent Application Laid-open Publication No. HEI 1-247786 (Patent Publication 1) discloses a system structured to set the pressure within a cylinder chamber at a high level, and the pressure within a back-pressure chamber on a back surface of a blade at a intermediate level, and to move the blade away from a roller by a pressure difference between the high pressure and the intermediate pressure for performing the uncompressed operation.
Japanese Patent Application Laid-open Publication No. HEI 6-58280 (Patent Publication 2) discloses the system provided with the discharge pressure chamber at one side of the blade, which is structured to reduce the pressure within the back-pressure chamber on the back surface of the blade at the low level such that the blade is pressed against the counter discharge pressure chamber under the high pressure of the discharge pressure chamber, and the blade is moved away from the roller by the pressure difference between the low pressure of the back-pressure chamber and the pressure of the cylinder chamber under compression for performing the uncompressed operation.
However, in the Patent Publication 1, as the pressure difference between the cylinder chamber and the back-pressure chamber on the back surface of the blade is small during the uncompressed operation, it is necessary to make small the spring constant of the spring member for urging the blade against the roller during the normal operation so as to move the blade away from the roller during the uncompressed operation. In the aforementioned case, the blade may jump (momentarily moving away from the roller) during the normal operation, resulting in the causing of noise or damage to the blade. In the system disclosed in Patent Publication 2, the high pressure within the discharge pressure chamber gradually leaks to the back-pressure chamber during the uncompressed operation, and the pressure within the cylinder chamber becomes gradually low. As a result, the blade cannot be held retracted, thus failing to continue the uncompressed operation.